German Published Patent Application No. 33 14 899 describes an electromagnetically operable fuel injector in which an armature cooperates with an electrically energizable solenoid for electromagnetic operation, and the lift of the armature is transmitted via a valve needle to a valve-closure member. The valve-closure member cooperates with a valve-seat surface to form a sealing seat. The armature is not rigidly attached to the valve needle, but instead is situated on it so it is axially movable. A first restoring spring acts upon the valve needle in the closing direction and thus keeps the fuel injector closed when the solenoid is currentless and not energized. The armature is acted upon by a second restoring spring in the direction of lift so that in the resting position, the armature is in contact with a first stop provided on the valve needle. On energization of the solenoid, the armature is moved in the direction of lift and entrains the valve needle beyond the first stop. When the current energizing the solenoid is switched off, the valve needle is accelerated into its closed position by the first restoring spring and entrains the armature past the stop described above. As soon as the valve-closure member strikes the valve seat, the closing movement of the valve needle is terminated abruptly. The movement of the armature that is not rigidly connected-to the valve needle is continued in the direction opposite the direction of lift and is absorbed by the second restoring spring, i.e., the armature swings back against the second restoring spring which has a much lower spring constant than the first restoring spring. The second restoring spring finally accelerates the armature again in the direction of lift.
When the armature strikes the stop on the valve needle, it may result in a renewed brief lifting of the valve-closure member connected to the valve needle from the valve seat and thus to brief opening of the fuel injector. Debouncing in the fuel injector referred to in German Published Patent Application No. 33 14 899 is therefore incomplete. Furthermore, a disadvantage of the conventional fuel injector in which the armature is rigidly connected to the valve needle, as well as with the fuel injector referred to in German Published Patent Application No. 33 14 899 is that the opening lift of the valve needle begins immediately as soon as the magnetic force exerted by the solenoid on the armature exceeds the sum of the forces acting in the closing direction, i.e., the spring closing force exerted by the first restoring spring plus the hydraulic forces of the fuel under pressure. This is a disadvantage inasmuch when the current energizing the solenoid is turned on, the magnetic force has not yet reached its final value because of the self-induction of the solenoid and the resulting eddy currents. The valve needle and the valve-closure member are therefore accelerated by a reduced force at the beginning of the opening lift. This results in an opening time which is not satisfactory for all applications.
In the closing movement, the conventional one-part armature adheres to the magnetized internal pole for a relatively long time and is released only after a relatively long time due to the residual magnetization. This results in relatively long closing times.